TWI499579B - Production of aromatic carboxylic acids - Google Patents

Description

Manufacture of aromatic carboxylic acids

This invention relates to methods and systems for the manufacture of aromatic carboxylic acids, such as purified terephthalic acid (PTA). One aspect of the invention pertains to a more efficient method of making aromatic carboxylic acids. Another aspect relates to a method of reducing the amount of effluent produced by the manufacture of aromatic carboxylic acids.

Aromatic polycarboxylic acids, such as terephthalic acid, are important chemical intermediates used in the manufacture of industrially important products, including polyester polymers, which can be used in the manufacture of fibers and in the manufacture of containers, bottles and others. Molded items.

Purified terephthalic acid (PTA) can be produced in a two-stage process. The prior art for the manufacture of terephthalic acid involves the liquid phase oxidation of aromatic feedstocks (such as para-xylene) using molecular oxygen in a solvent. Oxidation solvent comprises a lower (e.g. C ₂ -C ₆₎ aliphatic carboxylic acid (typically acetic acid) and water, in the presence of dissolved heavy metal catalyst system usually incorporating accelerator (such as bromine). Acetic acid is especially useful as a solvent because it has relative oxidation resistance and increases the activity of the catalytic pathway for oxidizing the aromatic starting material and the reaction intermediate. The reaction is carried out in one or more stirred vessels at a high temperature and pressure in the range of from about 150 ° C to 250 ° C and from 6 bar A to 30 bar A, respectively, and the crude terephthalic acid is typically produced in high yields (eg, at least 95%). (CTA). Under these conditions, CTA is precipitated from the solvent in the oxidation reactor to form a slurry of CTA solids in an oxidizing solvent which is maintained in suspension by agitation in the reaction vessel. The slurry temperature is lowered by passing through a series of crystallizers, each of which is under a decreasing pressure, and then the CTA solid is separated from the oxidation reaction solvent to obtain an oxidized mother liquor. The separation of the CTA solids from the oxidative mother liquor is carried out under positive pressure or under vacuum.

The solvent used for liquid phase oxidation is typically an aqueous solution of acetic acid and contains water produced by the oxidation of p-xylene and other reactive precursors. The oxidation reaction is an exothermic reaction and produces an aromatic carboxylic acid, a reaction intermediate which partially oxidizes the aromatic raw material, and by-products, which include chromogenic compounds, volatile components (such as methanol, methyl acetate, and methyl bromide). And degradation products such as carbon dioxide, carbon monoxide (carbon oxides) and benzoic acid (BA).

The second stage of the manufacturing process is the purification of CTA by catalytic hydrogenation in aqueous solution. CTA solids are typically dissolved in water at high pressure (70-90 barA) and elevated temperature (275-290 °C) and hydrogenated via a palladium on carbon fixed bed catalyst. The resulting solution was cooled by passing through a series of crystallizers in which purified terephthalic acid (PTA) was crystallized. The resulting slurry at a temperature in the range of about 140-160 ° C is fed into a suitable continuous solid-liquid separation device, such as a centrifuge or a rotary filter, where the PTA solids are separated from the purified mother liquor stream, washed and subsequently dry.

The oxidation reaction maintains the constant temperature by evaporating the oxidizing solvent exiting the reactor and returning the condensed solvent which can also be further cooled back to the reactor. In this way, the oxidation reaction mixture is cooled by the latent heat of the oxidizing solvent. The gas phase remaining in the reactor at the time of exhaust gas usually contains vaporized acetic acid, water vapor and volatile reaction by-products, as well as non-condensable components, including residual oxygen and nitrogen which are not consumed by the oxidation reaction (when air is used for oxidation reaction) When the molecular oxygen source is) and carbon oxides.

The water in the oxidizing solvent in the oxidation reactor typically forms condensate by condensing the off-gas of the oxidation reactor, separating the condensate from the remaining gas stream and separating at least a portion of the water from the remainder of the liquid condensate, followed by condensing the remaining liquid back. The reactor was used as an oxidizing solvent to maintain a constant content. Excess water separated from the condensate can be fed into the effluent treatment unit for disposal.

The separation of water from the oxidation reactor off-gas condensate can be most easily carried out by distillation, with a stream rich in low carbon aliphatic monocarboxylic acids as the bottom product and a water-rich stream as the top product. The previous modification of the manufacturing process was to remove the initial condensation step and to feed the oxidation reactor off-gas directly into the rectification column. The column may be placed above the oxidation reactor for direct return of the low carbon aliphatic monocarboxylic acid-rich stream to the oxidation reactor, although other configurations may be used.

The oxidation reactor is operated at high pressure and high temperature, and the exhaust gas of the oxidation reactor can be used to recover energy downstream of the rectification column. Energy recovery can be direct or indirect; it can be recovered by heat exchange, such as by raising the vapor for use elsewhere in the process, or by reducing the pressure of the gas stream by a machine such as an expander. The expander can be used to recover energy, such as driving an air compressor to feed air into an oxidation process or to generate electricity.

To purify terephthalic acid suitable for the manufacture of polyester polymers for the manufacture of fibers, bottles, containers and other molded products, the crude terephthalic acid is dissolved in water at elevated temperatures and pressures, followed by hydrogenation via a heterogeneous catalyst. The purification stage can be used to remove reaction intermediates and by-products known to cause coloration of the polyester polymer or to be associated with the coloration of the polyester polymer. In particular, the reaction intermediate p-toluic acid (p-Tol) (an aromatic monocarboxylic acid) is additionally formed by hydrogenation oxidation of the intermediate 4-carboxybenzaldehyde (4CBA), which is a PTA. Contaminants in the CTA must be reduced or eliminated. Since p-Tol is substantially soluble in water under the conditions used for purification, it remains substantially dissolved in the form of PTA solid crystals in a plurality of vessels and purification mother liquor downstream of the hydrogenation reactor, after which PTA solids and crystalline PTA are made. Slurry separation. Some p-Tol is co-crystallized with PTA, the amount of which depends on the process conditions. The p-Tol in a dissolved state reduces the yield loss of p-xylene to PTA and limits the use of the purified mother liquor as a water source at the manufacturing process.

In order to separate the low carbon aliphatic carboxylic acid from the water recovered in the form of oxidation reactor off-gas condensate, an appropriate number of separation stages are required in the rectification column and sufficient aqueous reflux is required at the top of the column. However, the total flow of aqueous reflux back to the top of the column is limited by maintaining the oxidation reactor water concentration at the target value. Typically, the aqueous reflux comprises a portion of the overhead product that remains in the top of the rectification column after condensation of the water-rich vapor stream. The remaining rectification column condensate (usually mostly water for the reaction) is then removed from the rectification overhead system.

Existing and alternative processes are the removal of a substantial portion of the overhead water condensate for use as a make-up water in the purification stage of the PTA manufacturing process, while providing a combination of pure equipment mother liquor and a smaller portion of the rectifier overhead condensate to Reflow in the rectifier. The pure equipment mother liquor contains significantly concentrated p-Tol, BA and other reaction intermediates and by-products, so the liquid stream returns to the following stages at the top of the rectifier column. The cleaner rectifier overhead condensate is returned to the top of the rectifier, and volatile impurities are removed from the pure equipment mother liquor refluxed from the rectifier overhead vapor stream, allowing subsequent overhead condensate to be reused in the process elsewhere. However, if the rectifier overhead condensate is used to supply most of the process water and if most or all of the pure equipment mother liquor is returned to the rectifier as reflux, then there is no disproportionate need in the scrubber at the top of the rectifier. In the case of the number of stages, the amount of water reflux provided by the rectifier overhead condensate is too low to remove volatile components from the pure equipment mother liquor and maintain the desired purity of the rectifier overhead condensate. In particular, the concentration of p-Tol and BA in the condensate at the top of the rectifier makes it unsuitable for use as a make-up water in the purification stage of the PTA manufacturing process, in which case water that is substantially free of such components is required. .

The combination of these problems reduces the economics of using a rectification column to separate water from the oxidizing solvent, which would otherwise allow water to be recycled between the oxidation and purification stages of the PTA manufacturing process and simplify the recovery of the oxidation reaction intermediate from the purification process. .

Therefore, there is a need for an improved rectifier as a method of operation of a distillation apparatus. In particular, it is desirable to have the water and process solvent advantageously separated from the oxidation reactor vent gas to recycle water between the oxidation stage and the purification stage, and to recover the oxidation reaction intermediate from the purification stage of the PTA manufacturing process.

In one aspect, a method of making an aromatic polycarboxylic acid is disclosed, comprising: a) separating an oxidation reactor vent stream into an acetic acid-rich gas stream and a water-rich vapor stream, wherein the water-rich vapor The stream comprises a volatile compound and a non-condensable gas, and the separation is carried out in a distillation apparatus; b) condensing the water-rich vapor stream into a condensate stream and a vapor stream; c) feeding the first portion of the condensate stream to the stream And distilling the second portion of the condensate stream into the extraction column; and d) removing the organic compound from the second portion of the condensate to form an organic product stream and an aqueous product stream. The distillation unit can be a rectifier.

At least part of the distillation unit overhead condensate may also be fed into the liquid-liquid extraction system to selectively remove organic components from the condensate into the organic liquid phase, leaving an aqueous phase with a low level of contaminants, which is suitable Used again elsewhere in the manufacturing process. There is no need to increase the separation responsibility of the distillation unit here, and the purification stage can be integrated with the oxidation stage of the PTA manufacturing process. It also reduces the amount of water fed into the effluent treatment unit. Additionally, the oxidation reaction intermediate can be recovered from the pure equipment mother liquor and recycled to the oxidation reactor. This increases the efficiency and conversion of the feedstock to the aromatic carboxylic acid product. The volatile organic components in the oxidation reactor off-gas are optionally recovered and recycled to the oxidation reactor.

In another aspect, a method of making terephthalic acid is disclosed, comprising: a) adding para-xylene, molecular oxygen, and acetic acid to an agitated oxidation reactor; b) removing the reactor from the oxidation reactor Exhaust gas, wherein the reactor vent gas comprises acetic acid and water vapor; c) feeding the reactor vent gas to a distillation column, wherein the reactor vent gas is separated into an acetic acid-rich gas stream (feeding it back to the oxidation And a water vapor-rich gas stream fed to the condenser; d) condensing the water vapor-rich gas stream into a condensate stream and a vapor stream, wherein the first portion of the condensate stream is fed back to the distillation a second portion of the condensate stream fed to the extraction column; e) feeding the vapor stream to the absorber to remove residual volatile components in the vapor; f) treating the paraxylene with the condensate stream The countercurrent direction of the second portion is fed into the extraction column; g) extracting the organic compound from the second portion of the condensate stream to form an aqueous stream, and feeding the organic compound into the oxidation reactor; h) Waterborne logistics feed into the water treatment tower Volatile components are removed, wherein the volatile components are recovered as vapor and condensed to form a reflux; i) the first portion of the reflux is fed back to the water treatment column and the second portion of the reflux Feeding back into the oxidation reactor; and j) feeding steam to the base of the water treatment column to remove residual volatile components, resulting in a fresh water stream that is substantially free of contaminants. The distillation column can be a rectifier.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning meaning meaning Any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

In one aspect, an improved method is disclosed for improving clean water used in a manufacturing process by recycling water from the remainder of the PTA manufacturing process and using it as a liquid reflux on top of the rectifier. Recovery rate.

The manufacture of aromatic carboxylic acids, including terephthalic acid, can be carried out in an agitated oxidation reactor. Here, an aromatic raw material (for example, p-xylene) is reacted with molecular oxygen which is usually derived from air, a reaction catalyst, and an aqueous acetic acid solvent to produce formic acid. The reaction temperature can be between about 150 ° C and about 250 ° C, including 190 ° C; and the pressure can be between about 6 bar absolute (barA) and about 30 bar A, including 13 barA. The CTA solid precipitated in the reactor as an oxidation reaction product and was maintained in suspension by an agitator. Other feed streams fed to the oxidation reactor may include reflux solvent, recycle solvent, recovered para-xylene, and recovered methyl acetate.

The slurry of CTA in the oxidizing solvent (mother liquor) flows to the crystallizer downstream of the oxidation reactor. The CTA solids are then separated from the oxidative mother liquor using a rotary filter, centrifuge or other similar device. The separation temperature is in the range of from about 90 ° C to about 160 ° C and the pressure is from about 0.6 bar A to about 4.5 bar A. The oxidation reaction intermediate can also be recovered from the pure equipment mother liquor and recycled to the oxidation reactor. This increases the efficiency and conversion of the feedstock to the aromatic carboxylic acid product.

The oxidation reaction is an exothermic reaction and the heat of reaction is removed by evaporating the solvent into a reactor effluent gas stream to the rectifier, which may be one or more vessels. The acetic acid and water in the reactor effluent gas are separated by distillation, which is operated at a distillation column overhead temperature in the range of from about 140 °C to 200 °C (including about 170 °C). Distillation can be carried out in a rectifier.

The aqueous reflux is supplied from the overhead condenser to the top of the distillation column, which may contain one or more heat exchangers. Additional aqueous reflux containing pure equipment mother liquor can be fed below the top of the column. The acetic acid-rich stream from the base of the column can be returned to the oxidation reactor. The column substrate is operated at substantially the same temperature as the oxidation reactor.

The water-rich vapor from the top of the column contains acetic acid (typically from 0.1 w/w to 5% w/w) which is condensed and cooled in stages to a temperature ranging from about ambient to about 100 ° C, including about 40 ° C. . A portion of the condensate, typically in the range of from about 130 ° C to about 160 ° C, is fed to the top of the column as an aqueous reflux. The overhead condenser may contain two or more heat exchangers, typically at least one heat exchanger for generating steam for efficient heat recovery from the top of the tower. The uncondensed gas passes through an absorber at about 6 barA to about 30 barA to remove volatile components such as para-xylene, methanol, methyl acetate, and benzoic acid remaining in the vapor.

The volatile component can be removed by contact with a liquid, first contacting an acetic acid-rich stream, such as an oxidizing solvent, and then contacting the water-rich stream. The washing liquid is fed into the oxidation reactor. The scrubbed effluent gas from the top of the absorber containing inert gas, including energy recovery, may be further processed in the range of from about 4 barA to about 28 barA (including about 11 barA), for example by passing through an expander, and subsequently discharged to the atmosphere. in.

Additionally, at least a portion of the overhead condensate can be fed to the liquid-liquid extraction system to selectively remove the organic components of the condensate into the organic liquid phase, leaving an aqueous phase having a low level of contaminants, which is suitable for Use it elsewhere in the manufacturing process. Here, a portion of the condensate at the top of the column is fed to the top of the extraction column, and fresh para-xylene can be fed to the bottom of the extraction column. Para-xylene acts as an organic phase extractant against the flow direction of the condensate as the aqueous phase upstream of the column, and the condensate flows below the entire liquid column. The aqueous phase and the organic phase are immiscible. The temperature of the organic phase and the aqueous phase can be controlled, and the paraxylene stream can be preheated. The organic compound comprising p-toluic acid, benzoic acid, methyl acetate, acetic acid and methanol dissolved in the aqueous phase is extracted into the organic phase, thereby substantially removing trace components and organic contaminants from the aqueous stream. The organic product at the top of the extraction column can be fed to the oxidation reactor as the primary source of para-xylene feed.

To recover the volatile organic component, as the aqueous product at the bottom of the extraction column enters the water treatment column, the aqueous product at the bottom of the extraction column is flashed and operated at near atmospheric pressure. The volatile component comprising para-xylene, methyl acetate and methanol is substantially separated from the aqueous stream and can be returned to the oxidation reactor. To enhance the separation of the volatile components from the aqueous phase in the water treatment column, steam can be fed to the bottom of the column. The water from the base of the water treatment column is substantially free of contaminants and can be used elsewhere in the manufacturing process, such as in purification equipment.

Figure 1 depicts one aspect of the disclosed process. Here, molecular oxygen is used to oxidize para-xylene to CTA in an agitated reactor containing one or more stirred vessels at elevated temperature and pressure. Specifically, the oxidation reactor 100 may be fed with air 200, an aqueous acetic acid solvent 201 containing a reaction catalyst, and p-xylene 220. The CTA solid precipitated in the reactor as an oxidation reaction product and was maintained in suspension by an agitator 101. Other feed streams fed to the oxidation reactor may include reflux solvent 204 from rectifier 102; recycle solvent 213 from absorber 105; and para-xylene, methyl acetate, and methanol recovered from water treatment column 108. 225. The oxidation reaction is an exothermic reaction and the heat of reaction is removed by evaporating the solvent into the reactor vent gas 202. Reactor product 203 (the slurry of CTA in an oxidizing solvent) is continuously passed to more than one crystallizer downstream of the oxidation reactor, followed by separation of the CTA solids from the oxidative mother liquor using suitable equipment.

The reactor off-gas 202 from the oxidation reactor 100 flows to the rectifier 102. The acetic acid in the reactor off-gas is separated from the water by distillation in a rectifier. The aqueous reflux is supplied to the top of the rectifier via stream 216, which is part of the condensate produced in overhead condensers 103 and 104 comprising one or more heat exchangers. An additional aqueous reflux 228 can be fed below the top of the rectifier, which contains the pure equipment mother liquor, which is produced by separating the PTA solids after crystallization in the purification stage. The acetic acid-rich stream 204 from the bottom of the rectifier can be returned to the oxidation reactor.

A water-rich vapor 205 containing a low level of acetic acid flows from the top of the rectifier to the rectifier overhead condensers 103 and 104. The condensers 103 and 104 contain two or more heat exchangers, at least one of which is used to generate steam for efficient heat recovery. The vapor 205 at the top of the rectifier is condensed and cooled in stages. Condensate 206 and 208 may be separated from the vapor stream at each condensation stage and, for example, via line 214 to overhead vapor line 207 to reflux drum 106, which may be at equilibrium pressure. A portion of the condensate collected in reflux drum 106 flows as aqueous reflux 215 and 216 to the top of the rectifier. Uncondensed gas 209 from the last heat exchanger is passed to absorber 105 to remove residual volatile components from the vapor. The volatile component is removed by contact with the liquid, including first contacting the acetic acid-rich stream (such as oxidizing solvent 210) and then contacting the water-rich stream 211. A washing liquid 213 containing acetic acid and water from the bottom of the absorber flows to the oxidation reactor 100. The scrubbed effluent gas 212 from the top of the absorber is passed forward for further processing, including energy recovery, and then vented to the atmosphere.

Condensate 217 and 218 collected in reflux drum 106 may also flow to the top of extraction column 107, and fresh para-xylene 219 may be fed to the bottom of extraction column 107. Para-xylene 219 can be heated in exchanger 111 to facilitate operation of extraction column 107. Para-xylene acts as an organic phase extractant against the flow direction of the condensate as the aqueous phase, flowing above the column, and the condensate flows below the entire liquid column. The aqueous phase and the organic phase are immiscible. The organic compound dissolved in the aqueous phase is extracted into the organic phase, thereby substantially removing trace components and organic contaminants from the aqueous stream. The organic product 220 from the top of the extraction column can be passed to the oxidation reactor 100 as the primary source of para-xylene feedstock in the reactor.

The bottom aqueous product 221 from the extraction column 107 flows to the water treatment column 108 where the volatile components are separated from the aqueous product and recovered in the overhead vapor 223, and the overhead vapor 223 flows to the condenser 109 where it condenses substantially. A portion of the condensate from the top of the water treatment column overhead condenser 109 is returned to the column as reflux 230, and the remaining condensate 225 can be returned to the oxidation reactor 100. The non-condensable vapor 224 from the water treatment tower overhead condenser 109 can be withdrawn from the system.

To ensure separation of the volatile components from the aqueous phase, steam 222 can be fed to the bottom of the water treatment column 108. The water from the water treatment column substrate is substantially free of contaminants and can be used as a fresh water supply 227 at the manufacturing process and is particularly useful in the purification apparatus 110. Excess water 226 can be sent to the effluent treatment before or after any other treatment.

Instance

The following examples further illustrate the invention.

The combination of physical measurements and models yields the results in the examples.

Example 1

The rectifier was configured as shown in Figure 1 to accept the effluent gas from the CTA oxidation reactor and reflux the acetic acid-rich stream to the reactor. The overhead stream of the condensing rectifier is substantially condensed and a portion of the condensate is returned to the top of the rectifier as a liquid reflux and the remaining condensate is fed to the extraction column. The organic phase from the extraction column (stream 220) contains para-xylene and is fed as a feed to the CTA oxidation reactor. The aqueous phase from the extraction column is fed to a water treatment column where the volatile components are separated from the aqueous product to produce water that is substantially free of contaminants and can be used as fresh water replenisher (stream 227) at the manufacturing process. Used and especially used in purification equipment.

Table 1 shows the concentration of aromatic monocarboxylic acids (i.e., contaminants) at key locations in the PTA manufacturing process. The recirculating water must have very little contaminants to act as water for washing the PTA. The aromatic monocarboxylic acid comprising benzoic acid and p-toluic acid is a conventionally monitored contaminant in the manufacturing process and must not exceed the target requirements of the final PTA product.

Comparative example 1

The system was configured as in Example 1, but there was no extraction step to remove organic components from a portion of the rectifier overhead condensate prior to the water treatment column.

Table 1 shows the increase in the content of aromatic monocarboxylic acids at key locations in the PTA manufacturing process compared to Example 1. The aqueous stream from the bottom of the water treatment column contains a large amount of organic components (such as aromatic monocarboxylic acids) and can no longer be used in place of the clean water in the PTA manufacturing process. For example, washing the PTA solids with an aqueous stream at the bottom of the water treatment column after separation from the mother liquor of the purification equipment will exceed the product requirements for contaminants containing aromatic monocarboxylic acids.

Example 2

The system was configured as in Example 1, but the rectifier has a lower separation capacity due to the reduced number of theoretical stages.

As shown in Table 1, the various aspects of the disclosed process result in a reduction in volatile aromatic monocarboxylic acid contaminants during various stages of the PTA process when compared to known processes. The disclosed process allows PTA to be manufactured cost effectively at a lower cost.

While the invention has been described in connection with the specific embodiments thereof Accordingly, the present invention is intended to embrace all such alternatives, modifications and modifications

100. . . Oxidation reactor

101. . . Agitator

102. . . Rectifier

103. . . Tower top condenser

104. . . Tower top condenser

105. . . Absorber

106. . . Reflux tank

107. . . Extraction tower

108. . . Water treatment tower

109. . . Water treatment tower overhead condenser

110. . . Purification equipment

111. . . Exchanger

200. . . air

201. . . Acetic acid aqueous solvent

202. . . Reactor exhaust gas

203. . . Reactor product

204. . . Reflow solvent

205. . . Water-rich vapor

206. . . Condensate

207. . . Tower top steam line

208. . . Condensate

209. . . Uncondensed gas

210. . . Oxidizing solvent

211. . . Water-rich logistics

212. . . Washed exhaust gas

213. . . Washing liquid / recycling solvent

214. . . Pipeline

215. . . Aqueous reflux

216. . . Aqueous reflux

217. . . Condensate

218. . . Condensate

219. . . Paraxylene

220. . . Organic product stream

221. . . Bottom aqueous product

222. . . steam

223. . . Top vapor

224. . . Non-condensable vapor

225. . . Recovered para-xylene, methyl acetate and methanol

226. . . Excess water

227. . . Water supply

228. . . Additional aqueous reflux

230. . . Reflux

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic process diagram of one aspect of the disclosed process illustrating the continuous oxidation process of the rectifier and extractor configuration.

100. . . Oxidation reactor

101. . . Agitator

102. . . Rectifier

103. . . Tower top condenser

104. . . Tower top condenser

105. . . Absorber

106. . . Reflux tank

107. . . Extraction tower

108. . . Water treatment tower

109. . . Water treatment tower overhead condenser

110. . . Purification equipment

111. . . Exchanger

200. . . air

201. . . Acetic acid aqueous solvent

202. . . Reactor exhaust gas

203. . . Reactor product

204. . . Reflow solvent

205. . . Water-rich vapor

206. . . Condensate

207. . . Tower top steam line

208. . . Condensate

209. . . Uncondensed gas

210. . . Oxidizing solvent

211. . . Water-rich logistics

212. . . Washed exhaust gas

213. . . Washing liquid / recycling solvent

214. . . Pipeline

215. . . Aqueous reflux

216. . . Aqueous reflux

217. . . Condensate

218. . . Condensate

219. . . Paraxylene

220. . . Organic product stream

221. . . Bottom aqueous product

222. . . steam

223. . . Top vapor

224. . . Non-condensable vapor

225. . . Recovered para-xylene, methyl acetate and methanol

226. . . Excess water

227. . . Water supply

228. . . Additional aqueous reflux

230. . . Reflux

Claims (16)

An aromatic polycarboxylic acid production process comprising: a) separating an oxidation reactor off-gas stream into an acetic acid-rich gas stream and a water-rich vapor stream, wherein the water-rich vapor stream comprises volatile compounds and non-corresible Condensing the gas, and the separating is carried out in a distillation apparatus; b) condensing the water-rich vapor stream into a condensate stream and a vapor stream; c) feeding a first portion of the condensate stream to the distillation unit and flowing the condensate stream The second portion is fed to the extraction column; and d) at least one aromatic monocarboxylic acid is removed from the second portion of the condensate to form an aromatic monocarboxylic acid stream and an aqueous product stream. The method of claim 1, wherein the distillation apparatus is a rectifier. The method of claim 1 or 2, further comprising e) feeding the aromatic monocarboxylic acid stream to the oxidation reactor. The method of claim 1 or 2, further comprising feeding the acetic acid-rich stream to the oxidation reactor. The method of claim 1 or 2, wherein the at least one aromatic monocarboxylic acid is removed from the second portion of the condensate using a liquid-liquid extractant. The method of claim 5, wherein the liquid extractant is an aromatic raw material oxidized in the oxidation reactor. The method of claim 5, further comprising e) separating the volatile product from the aqueous stream to produce a stream of water substantially free of contaminants. The method of claim 7, wherein the generated water stream is used as clean water in the manufacture of an aromatic carboxylic acid. The method of claim 8, wherein the aromatic carboxylic acid is terephthalic acid. The method of claim 9, wherein the liquid extractant is para-xylene. The method of claim 1, wherein the at least one aromatic monocarboxylic acid is selected from the group consisting of benzoic acid, p-toluic acid, and m-toluic acid. The method of claim 5, wherein the height of the distillation apparatus or rectifier is reduced by reducing the number of separation stages and reducing the separation responsibilities of the apparatus or rectifier. The method of claim 1 further comprising separating the oxidation reactor vent stream into a residual vent stream, wherein energy is recovered from the residual vent stream. The method of claim 13, wherein the energy recovery is performed by a mechanical device. The method of claim 14, wherein the mechanical device is an expander. The method of any one of clauses 13 to 15, wherein the recovered energy is available for power generation.